The present invention relates to a high density multilayer circuit board, each of the layers of which is accessible by blind via-holes, and more particularly, the invention relates to a high density multilayer circuit board prepared by a photo via-hole forming process, using an incombustible aqueous developing solution, and a photosensitive epoxy resin composition having a preferable resolution, plating solution resistance and heat resistance.
Varioud photosensitive epoxy resin compositions are well known widely such as the ones disclosed in JP-B-49-17040 (1974), JP-A-50-158694 (1975), JP-A56-55420 (1981), JP-A-63-71840 (1988), and others.
Most of the photosensitive epoxy resin compositions require organic solvents for their development. Chlorine group organic solvents cause many problems, such as water pollution, and therefore, an organic solvent for general use must be used at present. However, the use of an organic solvent inherently has the danger of producing a fire and explosion.
In accordance with the method disclosed in JP-A-63-71840 (1988), development with an alkaline aqueous solution is possible by using polyphenol resin as a base polymer. However, when the photosensitive layer contains so many hydroxyl groups as to be dissolved by the alkaline aqueous solution, the prepared relief pattern is caused to swell or become deformed in a chemical plating solution, which is a kind of alkaline aqueous solution, or there is a possibility that the plating solution will become contaminated by dissolving polyphenol into the plating solution.
On the other hand, the mounting of parts on the surface of a printed circuit board by a solder-reflow process has been used widely in order to mount the parts with a high density. Therefore, a thermally stable thermosetting resin, such as an epoxy resin and the like, has been used as the material of the substrate.